1. Field of the Invention
The present invention relates to the field of analysis of composite material, and more specifically to the nondestructive analysis of the loading and dispersion of reinforcing material in a composite material.
2. Description of the Related Art
Composite materials are an important segment of the structural materials market. The high specific strength and specific stiffness characteristics of some composite systems make composite materials particularly valuable. However, due to the inherent nature of composite materials, their properties are extremely sensitive to the materials' microstructure. A composite material may be characterized as a multiphase structure combining one or more reinforcing materials in a matrix. Variations in distribution, orientation, or amount of reinforcing material or matrix content from point to point in a sample of the composite material can give rise to large differences in material properties. In addition, the composite material used in the manufacture of parts is in many cases fabricated at the time of manufacture. Any material defects are thus incorporated in the final manufactured part, allowing no chance for elimination of these defects prior to manufacture.
To control the quality of the composite material, it is necessary to control the level of loading of the reinforcing material. It is also especially important to control the quality of dispersion of the reinforcing material, since dispersion affects material properties as well as appearance. Nondestructive evaluation techniques offer a potential means of identifying such properties without destroying the sample or the part of composite material.
Generally, destructive techniques are used to determine percent loading. The most common method is to weigh and ash the samples. This process takes as long as 40 minutes per sample and is not suitable, for example, for glass-reinforced fluoropolymers because the matrix of fluoropolymers reacts with the glass at the elevated temperatures associated with ashing. Ultrasonic (non-imaging) equipment is available commercially and can perform nondestructive analysis for generating a low-resolution map showing variations in matrix content across the surface of a sample. However, this equipment does single point measurement and is extremely slow. Also, it is necessary to calibrate this equipment with a set of known calibration samples, which is time-consuming.
Dispersion is ordinarily determined qualitatively. Nondestructive techniques for determining dispersion qualitatively include ultrasonic or film-based radiographic imaging. With ultrasonic imaging techniques, interpretation of the images is at best a slow and highly subjective procedure. Radiographic imaging using silver-based photographic film requires development of the film and then interpretation of the image, which is also subjective. Nevertheless, it can uncover gross defects, such as agglomerations and stress risers.
Dispersion may also be determined quantitatively. For instance, dispersion may be determined by multiple sampling and ashing of small sections of samples. However, this is a tedious and time-consuming procedure. Also, computed tomography may be used to determine fiber dispersion characteristics, as disclosed in Japanese Patent Application Publication Kokai 63-67551. This Publication discloses a method of evaluating the fiber dispersion characteristics in a fiber-reinforced composite material based on the histograms of cross-sectional images produced by X-ray transmission computed tomography. However, this approach uses reconstructive imaging techniques to produce a final image; consequently, it is expensive and is not able to give instantaneous feedback.
It is therefore an object of the present invention to provide a nearly instantaneous, quantitative, nondestructive method which does not rely on reconstructive imaging techniques for analyzing the loading and/or the dispersion of reinforcing material in a sample of composite material and an apparatus for performing this method.
It is also an object of the present invention to provide such a method and apparatus for analyzing the dispersion and/or the loading of reinforcing material in a composite material from which a final part has been manufactured.
It is further an object of the present invention to provide a method and an apparatus which can simultaneously analyze both dispersion and loading of reinforcing material in a sample of composite material.
Still another object of the present invention is to provide an apparatus and a method for producing and digitizing a film-based radiographic image of a sample of composite material to analyze the dispersion and/or loading of the reinforcing material in the sample.
Yet another object of the present invention is to provide a method for mapping the variation in the amount of reinforcing material in a composite material using either a radioscopic or a radiographic image of a sample of the composite material.
Additional objects and advantages of the invention will be set forth in the description which follows, and in part will be obvious from the description, or may be learned by practice of the invention. The objects and advantages of the invention may be realized and obtained by means of the instrumentalities and combinations particularly pointed out in the appended claims.